The present invention relates to methods and devices for squelching an audio output from a radio, and more particularly to a device and method for controlling HF radio squelch operation in which a serial tone burst indicates the start and end of a transmission and identifies an on-going transmission.
Transmission of radio signals, particularly high frequency (HF) signals, is subject to a number of degradations over which the operators have little, or no, control, such as noise, interference, and fading. These degradations may be heard as unwanted sounds in an audio output of a radio receiver, and are controlled to the extent possible with a squelching device. The determination when to activate the squelching device can be important in that inopportune timing of the activation of the device can lead to loss of the desired signal.
Traditional approaches to the problem of squelching device operation, particularly in HF single side band (SSB) radios, have included active squelching techniques in which a pilot tone is transmitted with the desired signal. The pilot tone is selected to be easily detectable and is excised with a notch filter at the radio receiver. However, the pilot tone decreases the amount of transmitted power available for the desired signal. Further, where data are sent with the pilot tone to provide control signals to a receiver squelching device, the SSB channel bandwidth is restricted. As is known, reducing the bandwidth available for voice transmission reduces intelligibility.
Accordingly, it is an object of the present invention to provide a novel method and device for controlling radio squelch operation that obviates the problems of the prior art.
It is another object of the present invention to provide a novel method and device for controlling HF SSB radio squelch operation in which a serial tone burst indicates the start and end of a transmission and identifies an on-going transmission.
It is yet another object of the present invention to provide a novel method of activating a radio receiver that is in a low power consumption sleep mode and of determining whether to squelch an audio output from the receiver in which three sets of serial tone based burst waveforms activate a radio receiver and deactivate squelch, maintain squelch deactivated, and indicate the end of a signal and activate squelch.
It is still another object of the present invention to provide a novel method of providing serial tone bursts at random times after activation of the radio receiver in which squelch is activated if a predetermined number of the serial tone bursts are not received within a predetermined period of time.
It is a further object of the present invention to provide a novel device for selectively operating a radio receiver squelching device in response to receipt of serial tone bursts contained within a transmission received by the receiver, where the bursts include a signal indicating whether the squelching device is to mute the receiver's audio signal.
It is still a further object of the present invention to provide a novel device and method for determining whether to squelch or unsquelch audio output from a radio receiver in which serial tone bursts include a signal indicating whether to squelch or unsquelch the audio output.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.